1. Field of the Invention
The present invention relates to a method of making a thin film device comprising a thin film, such as an amorphous silicon thin film, on a substrate. The present invention is suitable for a device wherein active or inactive devices on the substrate are disposed in one or other states for integration and extension. More particularly, the present invention is suitable in an amorphous type silicon solar battery wherein many element batteries are series connected.
2. Description of the Prior Art
As is hitherto known, integrated circuits are made by integration of diodes, transistors, etc. on a single crystalline silicon substrate, but their problem has been their high prices since thay are of 2-dimensional construction on expensive silicon single crystalline substrates in which very shallow surface parts only have been utilized. In recent years, in order to improve integration of the semiconductor devices, various proposals have been made. Among such proposals, a three-dimensional circuit construction has been proposed. One example of such proposed construction is to bore openings through an epitaxially grown single crystalline layer and vapor deposit thereon so as to make a contact with the underlying electrode or layer. But the method is not easy, and has not been brought into actual use because of its having many troublesome steps.
On the other hand, a thin film solar battery which has an opto-electronic conversion thin film on a substrate is exemplified by the amorphous silicon solar battery, wherein many unit cells are series connected on the substrate as shown by FIG. 1(a), which is a schematic perspective view of a conventional series connected solar battery. In FIG. 1(a), several first electrodes 2 of a transparent conductive film with a predetermined pattern are formed on a transparent substrate 1. A thin film 3 consisting of amorphous silicon layers of known P-I-N structure of strip shape is formed on each of the first electrodes 2. A second electrode 4 is formed on each of the thin films and on the laterally extended part of the first electrode 2 of the next cell. In this conventional device, the front end parts 5 of FIG. 1(a) constitute series connections, where each first electrode, a second electrode disposed thereover and a thin film inbetween forms one solar battery cell; and each first electrode 2 is connected to the second electrode 4 of the next cell at the front end portions, thereby making series connections of the solar battery cells. With the construction as shown in FIG. 1(a), when the size of the device becomes large and therefore the length l of each of their film devices becomes large, then the average length of the current path becomes long, thereby increasing the series resistance of the overall device.
Another exemplary conventional device is shown in FIG. 1(b), wherein strip shaped and parallel disposed transparent first electrodes 7 are formed on a transparent substrate 6, thin films 8 of amorphous silicon of P-I-N layer structure of strip shaped pattern are disposed on the transparent first electrode 7, and further thereon strip shaped second electrodes 9 are formed. The first electrode 7 and the second electrodes 9 are formed and connected as follows: Each first electrode 7 extends slightly leftward for all of its length beyond the coverage by the corresponding thin film 8 thereon. Each thin film 8 is formed slightly rightward beyond the right end of the first electrode 7 thereby to touch the substrate 6. Each second electrode 9 extends slightly rightward for all of its length beyond the area over the corresponding thin film 8 thereunder. Thereby each second electrode 9 is connected with its right end portion to the left end portion part of the first electrode 7 of the next rightward cell, thereby making series connection of all the cells on the substrate, each along its whole length. Therefore, in this conventional device of FIG. 1(b), even though the length of the individual devices becomes large, this does not increase the current path. However, in this example, since the amorphous silicon is deposited by glow discharge in a relatively low vacuum of about 1 Torr, the discharge is disturbed by the pattern mask for forming the thin film amorphous silicon film in discrete strip shapes. Therefore, the precision of the thin film pattern is not sufficietnly high, thereby requiring a considerable area for isolating neighboring unit cells, and utility of the substrate area is limited. The problem of this prior art device is the necessity of a precise mask pattern for forming the amorphous silicon thin films, which is troublesome.